An automatic approach for selecting new Hα emission-line galaxies

Abstract

The most unambiguous way to discover new emission-line galaxies (ELGs) is directly by the presence of their lines, using objective-prism plates of adequate resolution. The first survey using this technique was developed by Smith in 1975 with the 0.6 m CTIO Curtis Schmidt Telescope. The Universidad Complutense de Madrid (UCM) is carrying out a survey of ELGs with the Schmidt Telescope at Calar Alto (Almería, Spain) using the presence of Ha in emission in IIIa-F prism plates as selection criterion. The observational procedure and results are described in Rego et al. 1989; Zamorano et al. 1990; Zamorano et al. 1993. The standard procedure is to scan the plates by eye, with a low-power binocular microscope. The use of different subjective criteria in the visual inspection can produce biased samples. Moreover, the visual scan does not produce any quantitative measure but only a sample of candidates. Therefore, in order to obtain an observer-independent sample and to extract the largest amount of information from the original plates, 2 plates have been scanned with the MAMA machine 1 (Guibert & Moreau 1991; Moreau 1992) with the aim of developing an automatic procedure to detect ELGs spectra.